Coordinate measuring machines operating in three axes of movement in conjunction with a microcomputer are commonly utilized to process measurement and dimensional data on components. Typically, such measuring machines include a rigid table comprising, for example, granite, upon which a workpiece is positioned. A moving bridge mounted on rails over the table supports a carriage having a rail that moves toward and away from the workpiece. The bridge moves across the table on the ways in one linear axis (the "X-axis") while the carriage moves perpendicularly to the X-axis along the bridge (the "Y-axis"). The carriage's control axis, the Z-axis, consequently, moves perpendicularly to the X- and Y-axes along the "Z-axis". "Control axis" is defined as the axis which the operator uses to control the motion of a coordinate measuring system when used manually. In the embodiment disclosed herein, this would be the Z-axis.
In operation, the moving components of the coordinate measuring machine are supported on their respective bearing surfaces that substantially minimize friction, thus allowing a user to move the lower end of the Z-axis or control axis in three dimensions by grasping the end and gently translating it in the desired direction. In this manner, a probe located at the end of the rail in a probe holder can be positioned at different points along the measuring piece. The probe can include an electronic or manual trigger that generates a signal each time the probe touches the surface of the workpiece.
The coordinate measuring machine is typically interfaced with a microcomputer or similar information storage and processing device. As the user moves the probe across the workpiece, triggering point signals, the computer records the relative spatial position of the probe, This information is typically obtained by determining the position of the bridge, the carriage and the Z-axis with respect to each of the machine's X, Y and Z bearing surfaces.
The measuring process described above is often slowed by the user's interaction between the probe and the computer. For example, most measuring routines require the user to select, by means of a keyboard, light pen or other computer interface, a particular measuring operation to be performed and a particular geometric shape to be measured by that operation. To select the operation, the user must interact directly with the computer terminal while, usually, taking his or her hands off of the probe holder. Following selection, the user then returns to the probe holder and performs the measuring operation on the workpiece. Subsequent to obtaining a particular group of points or "measuring block", the user then typically returns to the computer terminal to process the measuring block. Such processing can include entry of the points, cancellation of the points, re-entering of certain points, comparison of the points to known values and/or application of tolerance ranges to the points. Subsequent to processing of the measuring block, the user then selects another measuring operation, such as a further measurement on the same workpiece, and repeats the measuring process by moving the probe accordingly.
The user's continual shift from the measuring machine, to the computer terminal, and back, substantially increases the overall time devoted to measuring a workpiece. One attempt to reduce user interaction time resulting from the need to shift between the measurement device and the computer terminal is embodied in the System 6.TM. by Romer of Montoire, France. The System 6.TM. is an articulated arm measuring device having two elongated hinge members at the base of the unit and a shorter hinge member with a wrist joint at the probe end of the unit. It is used primarily to measure large objects and moves in six degrees of freedom (6 axes). The System 6.TM. includes a switch that allows the user to change between measuring mode and computer data entry mode. As such, when the data entry mode is activated, the wrist and end hinge become, essentially, joystick controllers that generate data signals to allow a cursor to be manipulated on the computer screen. The user usually backs the probe away from the workpiece so he or she has ample room to manipulate the arm in its "joystick" capacity. Once data entry is accomplished, the user switches back to measurement mode, returns the probe to the workpiece and continues his or her measurements. The ease with which the articulated arm can be moved out of interferring contact with a workpiece, and the overall scale of the device make such multi-tasking of arm joints practical. However, such a device would be unsuitable for a three-axis measuring machine.
In view of the disadvantages of the prior art, it is an object of this invention to provide a computer interface device that allows the user to maintain control of the measuring machine probe while operating the computer. The interface should not interfere with conventional operation of the measuring machine and should be readily adaptable to existing measuring machines, computers and overall systems.